Cathode and heater structure for electron tubes



Dec. 4, 1951 w. w. EITEL EI'AL 2,577,239

CATHODE AND HEATER STRUCTURE FOR ELECTRON TUBES 2 SHEETS-SHEET 1 Filed Sept. 12, 1949 a v M w 3 Q a 2 9 6 3 5 3 7 5 M a m 4 INVENTORS Will/am 14 E/fe/ ATTORNEY Dec. 4, 1951 Filed Sept. 12, 1949 w. w. EITEL ETAL CATHODE AND HEATER STRUCTURE FOR ELECTRON TUBES 2 SHEETS-SHEET 2 Es rE 52- :35 s 9: Q5 INVENTORS W/l/iam W. E/fe/ 58 BY .Haro/d QMi/ler lig :7 7

ATTORNEY Patented Dec. 4, 1951 CATHODE AND HEATER STRUCTURE FOR ELECTRON TUBES William W. Eitel, Woodside, and Harold D. Miller,

San Bruno, Calif laugh, Inc., of California assignors to Eitel-McCul- San Bruno, CaliL, a corporation Application September 12, 1949, Serial No. 115,196 1 Claim. (01. 313-340) Our invention relates to an indirectly heated cathode and an improved heater structure for the same, adapted for cathodes such as those of the oxide coated type frequently used in electron tubes.

It is among the objects of our invention to provide an indirectly heated cathode incorporating a simplified and rugged heater structure.

Another object is to provide a heater unit which may be fabricated as a unitary structure apart from the cathode.

A further object is to provide an indirectly heated cathode of high thermal efliciency.

The invention possesses other objects and features of advantage, some of which with the foregoing, will be set forth in the following description of our invention. It is to be understood that we do not limit ourselves to this disclosure of species of our invention. as we may adopt variant embodiments thereof within the scope of the claim.

Referring to the drawings:

Figure l is a vertical sectional view of a tube embodying our improved heater structure; and

Figure 2 is a bottom view of the same.

Figure 3 is an elevational view, partly in section, showing the heater unit prior to assembly in the cathode.

In terms of broad inclusion our improved indirectly heated cathode comprises a metallic cathode sleeve, a heater unit comprising a metal liner fitted in the sleeve, and an insulated heater coil carried on the inner surface of the liner. In our preferred construction the heater coil is bonded to the inner surface of the liner by a layer of insulating material. The heater unit comprising the liner and heater coil is preferably fabricated apart from the cathode and subse quently inserted in the cathode sleeve.

In greater detail and referring first to Figures 1 and 2 of the drawings, our improved cathode is illustrated in conjunction with an electron tube of the type disclosed in the copending application of Donald F. Drieschman and Hubert H. Eaves, Serial No. 104,198, it being understood that our improvements may be incorporated in any type of tube having an indirectly heated cathode. The tetrode illustrated comprises an envelope having an upper section 2 and a lower section 3. The upper section comprises a cup-shaped blank 4 of a vitreous material such as glass having sealed to its lower edge a metal ring 6 provided with an outturned flange 1. The lower section 3 comprises a vitreous header 9 forming the bottom wall of the envelope and has sealed along its periphery a metal ring H with an outturned flange l2 registering with flange l of the upper section. Header 9 is preferably molded in the desired shape, as by melting powdered glass in a graphite mold. By such molded glass technique the various metal parts hereinafter described may readily be sealed in place during the molding operation. After the tube has been assembled the envelope sections are sealed together by a braze I3 about the periphery of flanges 1 and I2.

The electrodes are of concentric cylindrical construction comprising a cathode I4, control grid I 6, screen grid I! and anode l8. shaped metal anode I8 is supported from the upper envelope section 2 by a lead I9 extending coaxially with the axis of the tube. This lead is hollow and serves the dual function of providing a conductor for the anode and an exhaust tubulation for the envelope. Tubular body 2| of the lead is sealed to the upper portion of glass blank 4 and has a suitable fitting 22 at its lower end for fastening to the anode l8. A metallic exten sion 23 of the lead provides a connection to the exhaust system and, after evacuation of the envelope, is pinched ofi by compressing the walls of the tubing together at tip 24. Slots 26 in the lead serve to retard heat flow from the anode to the glass seal.

The cathode l4, control grid l6 and screen grid 11 are all mounted on the lower envelope section 3 so that these electrodes may be accurately assembled and aligned prior to the putting on of the upper half of the envelope. Cathode 14 comprises a sleeve or cylinder of metal such as nickel, preferably cup-shaped, having an electron emissive coating such as the barium-strontium oxide mixture commonly used for that purpose. The cathode is mounted on a circular support 21 sealed centrally in the header 9, this support being preferably cup-shaped with its lower portions embedded directly in the glass of the header. The flange of support 27 carries a sleeve 28 which in turn is connected to the cathode by an interposed sleeve 29. This latter sleeve is of thin metal having poor heat conductivity so as to thermally isolate the cathode from the header structure. A metal rod 30 connected to the lower end of support 21 preferably projects out through the bottom of header 9 for the purpose of carrying heat out from the cathode supporting structure. Layers of corrugated sheets 36 at the top provide additional heat shielding and are preferably of a metal such as zirconium having gettering or gas-absorbing properties, the upper The cupend of the cathode being preferably recessed to retain these disks.

Control grid l3 and screen grid [1 which surround the cathode are preferably of the cage type, fabricated of suitable wire, and are supported at their lower ends from the header structure. The control grid supports 31, say three in number, are arranged in a circle about the oathode support. These supports are sealed in the header and project upwardly into the envelope to carry the control grid mount 38. the latter being preferably conical in shape and having three legs connected to outtumed ends of the supports 31.

In a like manner a plurality of screen grid supports 39 are sealed in the header in a larger circle surrounding the cathode support and spaced alternately with respect to the control grid supports. The conical mount 4| for the screen grid has legs connected to the supports 39, which legs lie between those of the control grid mount. This structure provides a rugged mounting for the grids and reduces the capacitance effects between the grid supports.

Four terminal pins 42, 43, 44 and 45 are sealed in the header to project downwardly from the envelope and are arranged in a circle about the tube axis, the upper ends of these pins being embedded in the glass of the header. The interconnections between the terminal pins and electrode supports are preferably sealed wholly within the glass of the header to further enhance the compactness and ruggedness of the base structure. Thus the cathode pin 42 is connected to the rod 30 by a strap 46, the control grid pin 43 is connected to one of the supports 31 by a strap 41, and the screen grid pin 44 is connected to one of the supports 39 by a strap 48, which straps are embedded in the glass of the header. A post 49 connected to the heater pin 45 projects upwardly within the envelope to support the outturned end of a center rod 32, the latter extending through a slot 5| in cathode supporting sleeve 28.

In the above general description of the tube a cathode sleeve l4 which carries the emissive coating was mentioned, such cylindrical sleeve being representative of the kind of cathode sleeve usually found in an indirectly heated type of cathode. Our improved cathode structure incorporating the cathode sleeve l4 will now be described.

The heater for sleeve 14 comprises a cylindrical metal liner 52, say of nickel, sized to make a close sliding fit with the cathode sleeve so that when inserted the liner fits snugly in surface-to-suriace contact with the interior face of the'cathode sleeve. An end plate or disk 53 secured to the lower rim of liner 52 provides a closure for the lower end of the heater structure. 7 An insulated coil 54 of refractory metal, say tungsten wire, is carried on the inner surface of the liner. In our preferred construction the coil is embedded or partially embedded in an insulating layer 56 which supports the convolutions of the coil and bonds the same to the inner surface of the liner, the layer 55 being of any suitable insulating material such as silica or alumina. A convenient method is to first apply the insulating material to the inner surface of the linerand the coil, as by coating with powdered material and firing in vacuum, and, after placing the coil in the liner, coating the parts with additional powder and firing again to build up the layer 56 and achieve the desired integrally bonded construction. One end of the heater coil is electrically connected to the liner as by welding at 51 and the other end provides a terminal connection 58 which is brought out through the end plate 53 at an insulating bead 59, the latter end being connected to the center rod 32.

Referring to Figure 3, which shows the heater structure separately, it is seen that the entire heater may be fabricated as a unit prior to assembly in the cathode. This is a decided advantage because the wire used in heater coils of this kind is usually of very small size, making it extremely diificult to assemble the coil in the cathode by the conventional methods of heater construction. In our heater unit the coil of fine wire has adequate mechanical support and is well protected by the metal liner 52 so that the completed unit may be safely handle while being mounted in the cathode. Another advantage is the simplicity of final cathode assembly since this operation is merely one of slipping the completed heater unit into the cathode sleeve.

Still another feature of our improved cathode structure is that heater coil 54 is closely associated with the cathode sleeve l4 to be heated. The close proximity of the heater coil together with the fact that liner 52 is in direct contact with sleeve l4, results in good heat transfer and high thermal efiiciency. A further advantage is that a tube embodying our cathode can withstand severe shock and vibration without danger of breaking or shorting out the heater.

We claim:

An indirectly heated cathode structure for an electron tube having an evacuated envelope, a cylindrical metallic cathode sleeve, a heater unit comprising a cylindrical metal liner fitted in the sleeve, and an insulated heater coil carried on and integrally united with the inner surface of the liner, said liner and insulated heater coil lying within the evacuated space of the envelope.

WILLIAM W. EITEL. HAROLD D. MILLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,599,180 McIlvaine Sept. 7, 1926 1,924,318 Hull et al Aug. 29, 1933 2,099,846 Farnsworth Nov. 23, 1937 2,199,675 Gustin June '7, 1938 2,227,046 Waldschmidt Dec. 31, 1940 FOREIGN PATENTS Number Country Date 303.037 Great Britain Dec. 27. 1928 

